OJECT SUMMARY (See instructions): Antibiotic resistant bacterial infections have become a major problem worldwide. Among Gram positive pathogens, invasive methicillin-resistant Staphylococcus aureus infections (MRSA) and vancomycinresistant enterococcal (VRE) infections represent particular threats. This proposal is a subproject in a Harvard-wide program to address the need to develop new approaches to overcome these infections. The four aims in this subproject are directed towards exploring new compounds, targets, and strategies to overcome MRSA and VRE. The first aim is to develop combined chemical and enzymatic methods to make novel phosphoglycolipid antibiotics that inhibit peptidoglycan (PG) biosynthesis by targeting the enzymes that make the glycan chains of PG. The second aim is to elucidate the pathway for wall teichoic acid (WTA) biosynthesis in Enterococcus faecalis and assess its potential as an antibacterial target in order to lay the groundwork for inhibitor screening. The third aim is to discover novel TarO inhibitors that can be used in combination with beta lactams to overcome MRSA infections. The fourth aim, to be carried out in collaboration with other subprojects, is to evaluate the compounds we discover in prioritized animal models. These studies will include evaluation of a 8. aureus-selective WTA-active antibiotic that we previously discovered and have already optimized for in vitro activity. The proposed research may lead to the development of new antibiotics for clinical use to treat MRSA and VRE infections.